Officials of the administration have begun to lay out the defense of the campaign to different audiences in recent days. Secretary of State Hillary Rodham Clinton and Secretary of Defense Robert M. Gates took to the airwaves over the weekend to make the case that the country has an interest in protecting its allies and promoting stability in the region.

White House officials have also begun rolling out a nuanced argument that the U.S. had a responsibility to act, relying heavily on the fact that there would be international cooperation on the effort.

But Obama's remarks were aimed at the American public as it tires of ongoing war on two other fronts and begins to voice skepticism about the wisdom of the airstrikes.

At its heart, Obama's message for Americans was a simple one. The U.S. will send no ground troops to Libya. It will not lay a new burden on taxpayers, but rather will absorb the cost of the effort in current Pentagon budget restraints.

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And if the military had not acted, there would have been a government massacre of civilians and a radical destabilization in the region -- with negative consequences for allies in Europe.

But those looking for a promise of military aid to other countries should read no precedent in the Libya intervention, aides to the president said Monday.

The U.S. doesn't intervene to keep with precedent or to follow "consistency guidelines," said one senior administration official, but rather to advance the nation's interests.

"Each of those interests is going to be unique in each instance," said deputy national security adviser Denis McDonough.

Still, a skeptical audience is looking for clues about how the president will engage the military as volatile events unfold in the Middle East and North Africa. While refraining from openly criticizing Obama's decision to dispatch military personnel to the region, Republicans in Congress want the president to state plainly what national security interest justified risking American lives.

"The president has failed to explain up to this point what follows the evident establishment of a no-fly zone over Libya, as it was originally described," Senate Republican leader Mitch McConnell of Kentucky said Monday. "The president has articulated a wider political objective of regime change in Libya that is not the stated objective of our military intervention, nor is it the mandate of the U.N. resolution that the president has used as a justification for our military efforts there."

In part, the answer has something to do with the memory of what happened in Rwanda, where in 1994 the presidential guard, military officials and politicians began a genocide that in just months wiped out 800,000 ethnic minorities.

Clinton, Ambassador to the United Nations Susan Rice and National Security Council aide Samantha Power have all spoken repeatedly of their deep regrets about the 1994 Rwanda killings, and pushed for the administration not to risk a repeat in Benghazi.

The three aren't the only ones thinking about the lessons of Rwanda: Obama himself has declared repeatedly how the massacres shaped his outlook. He has publicly supported the principle of and "responsibility to protect," which provides that the world community should intervene when a government allows, or causes, mass killings of its own.

At the same time, administration officials argued Monday that the closer comparison may be to the Bosnian war, in which NATO, the Western military alliance, intervened with limited airstrikes to prevent the slaughter of civilians.

And the Rwandan massacre was only one of several factors that led the administration, after weeks of hesitation, to decide to sign on for battle.